编写程序，初始化10名学生的基本信息，包括学号、姓名、三科（高数、英语、程序设计）成绩，分别计算每名学生的总分，并按个人总分对学生降序排序，输出排序后的学生信息。
下面是我写的代码：

#include <stdio.h>
struct courses
{
    char cName[20];
    double score;
};
struct student /* 学生信息结构定义 */
{
    int num;                     /* 学号 */
    char name[10];               /* 姓名 */
    double sum;              /* 平均分 */
    struct courses sc[10];
};
int main()
{
    int i=0, index, n, j;
    struct student students[10]={   {101,"xiao",{{1,"computer",89},{2,"math",78},{3,"english",76}}},
                                    {102,"zhao",{{1,"computer",89},{2,"math",78},{3,"english",76}}},
                                    {103,"qian",{{1,"computer",89},{2,"math",78},{3,"english",76}}},
                                    {104,"sun",{{1,"computer",89},{2,"math",78},{3,"english",76}}},
                                    {105,"li",{{1,"computer",89},{2,"math",78},{3,"english",76}}},
                                    {106,"zhou",{{1,"computer",89},{2,"math",78},{3,"english",76}}},
                                    {107,"wu",{{1,"computer",89},{2,"math",78},{3,"english",76}}},
                                    {108,"zheng",{{1,"computer",89},{2,"math",78},{3,"english",76}}},
                                    {109,"wang",{{1,"computer",89},{2,"math",78},{3,"english",76}}},
                                    {110,"jiang",{{1,"computer",89},{2,"math",78},{3,"english",76}}}
                                }, temp; /* 定义结构数据 */
    for (; i < 10; i++)
    {
        printf("num:%d\n",students[i].num);
        printf("name:%s\n",students[i].name);
        students[i].sum +=students[i].sc[10].score;
        printf("sum:%lf\n",students[i].sum);
    }
    /* 结构数组排序，选择排序法 */
    for (i = 0; i < n - 1; i++)
    {
        index = i;
        for (j = i + 1; j < n; j++)
        {
            if (students[j].sum > students[index].sum) /* 比较平均成绩 */
            {
                index = j;
            }
        }
        temp = students[index]; /* 交换数组元素 */
        students[index] = students[i];
        students[i] = temp;
    }
    /* 输出排序后的信息 */
    printf("num\tname\tsum\n");
    for (i = 0; i < n; i++)
    {
        printf("%d\t%s\t%d\n", students[i].num, students[i].name, students[i].sum);
    }
    return 0;
}

接下来就写不下去了，求和那里程序不能求和，然后下面的排序也对应 的出了问题。

求大佬帮我改正。